Domoic acid is the known causative agent responsible for amnesic shellfish poisoning (ASP). Although there is only one documented ASP case in the world, there is a potential of its occurrence in Southeast Asian countries. However, limited information on domoic acid producing diatoms is available except for Nitzschia navis-varingica, which is known to produce significant levels of domoic acid. In order to obtain fundamental data on domoic acid producing diatoms, screening of Pseudo-nitzschia and Nitzschia species were primarily performed in the Philippines. Two source areas, i.e. Manila Bay and Iba estuary of Luzon Island, were selected for observation of these diatoms. Fifty eight isolates of Pseudo-nitzscia and 18 isolates of Nitzschia-like diatoms were prepared from Manila Bay and Iba estuary, respectively. These isolates were cultured and tested for the production of domoic acid and its derivatives. Pseudo-nitzscia strains did not show any signs of domoic acid production. Five out of 18 Nitzschia isolates were confirmed to produce isodomoic acids A and B. Comparison of sonication and boiling in water bath as extraction methods was investigated and results showed that both methods yielded comparable amounts of domoic acid. Stability of domoic acid extracted by boiling was also investigated and was found out to be stable at room temperature for ten days. Results implied an advantageous and convenient way of sample preparation and preservation for international transport
